Catalytic poly(vinyl alcohol) functionalized membranes obtained by gamma irradiation M.H. Casimiro a,n , A.G. Silva a , J.V. Pinto b , A.M. Ramos a , J. Vital a , L.M. Ferreira c a REQUIMTE/CQFB, Departamento de Quı ´mica, Faculdade de Ciˆ encias e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal b Departamento de Ciˆ encia dos Materiais and CENIMAT/I3N, Faculdade de Ciˆ encias e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal c Unidade de Fı ´sica e Aceleradores, Instituto Tecnolo ´gico e Nuclear, ITN, 2656-953 Sacave´m, Portugal article info Article history: Received 26 August 2011 Accepted 25 January 2012 Available online 7 March 2012 Keywords: Polymeric catalytic membranes Gamma irradiation Poly(vinyl alcohol) Sulfonic groups Isoamyl acetate abstract Polymeric catalytic membranes bearing sulfonic acid functions have been prepared by mutual gamma irradiation at a 60 Co source, of poly(vinyl alcohol) (PVA) membranes and methanesulfonic acid. The effect of various synthesis conditions on membranes’ physical–chemical properties and catalytic activity in the esterification reaction between acetic acid and isoamyl alcohol to obtain isoamyl acetate (banana flavor), was evaluated. The membranes were characterized by ATR-FTIR, TPP, AFM and SEM. Water contact angle determinations were also performed. The obtained results showed that within the range of conditions studied the increase in sulfonic acid groups’ content is accompanied by an enhancement in the membranes catalytic activity, while the increase in absorbed dose leads to a decrease in catalytic activity. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction In recent years the use of polymeric catalytic membranes (PCM) which seek to combine chemical reaction and separation processes, has been showing a growing interest (Vankelecom, 2002; Ozdemir et al., 2006). PCM are not only a way of supporting an active catalyst but can also be tailored in order to magnify catalytic activity. Since a heterogeneous catalytic reaction occurs at the fluid–solid interface, the modification of the polymer crosslinking degree or the polymer hydrophilic/hydrophobic balance (e.g. by blocking or grafting hydro- philic functional groups), promotes changes in the membrane sorption and transport properties which can be optimized in order to maximize catalytic activity. A variety of acidic catalyzed reactions such as olefin hydration, alcohol dehydration, esterification and transesterification reactions, etc., have been carried out over sulfonated polystyrene (PS) resins (Armor, 2001; Tejero et al., 2002; Izci and Bodur, 2007; Shibasaki- Kitakawa et al., 2007). Poly(vinyl alcohol) (PVA) matrixes bearing sulfonic acid functions have also been reported as catalysts in the transterification of soybean oil (Guerreiro et al., 2006) in esterification of acetic acid with isoamyl alcohol (Castanheiro et al., 2006) and in the hydrolysis of sucrose (Pito et al., 2009). In all these cases, the sulfonic groups present in the acids used in the catalysts’ preparation are the active sites of the membranes. One of the advantages of PVA over PS relies on its much better permeability to water which makes it suitable for use in pervaporation processes (Vankelecom, 2002). However in the reported use of all matrixes mentioned above, the polymer modification was obtained by the traditional chemical synthesis. A clean and additive-free versatile alternative way for preparation of a wide variety of polymeric tailored materials is gamma irradiation. The novelty of the present work is the preparation of the modified polymers’ catalytic actives by using irradiation, a subject scarcely reported in literature. To our knowledge only the grafting promoted by UV irradiation of quaternary ammonium groups to polymeric membrane surfaces (Nunes and Peinemann, 2010), and the functionalization of polyethersulfone by electron beam graft- ing of polystyrene (Shah and Ritchie, 2005) are referred. Here, catalytic PVA matrixes bearing sulfonic acid functions were obtained by mutual gamma irradiation of PVA membranes and methanesulfonic acid (MS) and used as catalyst in the esterifica- tion reaction between acetic acid and isoamyl alcohol (Scheme 1), an interesting industrial reaction with the resulting product isoamyl acetate, which is the banana flavor used in food industry. Even under development our purpose has been to evaluate the effect of various synthesis conditions on membranes’ physical– chemical properties and on membranes’ catalytic activity. 2. Experimental 2.1. Preparation of PVA functionalized membranes PVA membranes were prepared by dissolving PVA (Aldrich, average molecular weight: 95,000; degree of hydrolysis: 98%) in Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/radphyschem Radiation Physics and Chemistry 0969-806X/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2012.01.036 n Corresponding author. Tel.: þ351 21 2948385; fax: þ351 21 2948350. E-mail address: m.casimiro@fct.unl.pt (M.H. Casimiro). Radiation Physics and Chemistry 81 (2012) 1314–1318